WASHINGTON (Reuters) - U.S. Secretary of State Rex Tillerson will press China and other Asian countries to take tougher action against North Korea when he attends regional meetings in Manila starting this week, a senior U.S. official said on Wednesday.

Susan Thornton, the acting assistant secretary of state for East Asia, said Tillerson would have the chance to engage with China's foreign minister at the meetings of the Association of Southeast Asian Nations in Manila, but had no plans to meet North Korea's foreign minister there.

Thornton said Tillerson, who is due in Manila on Saturday, would be seeking greater cooperation in isolating North Korea and in enforcing U.N. sanctions over its missile and nuclear weapons programs. She said Washington wanted to see countries "drastically" reduce their dealings with Pyongyang.

"What we are trying to do is galvanize this pressure and isolate North Korea so it can see what the opportunity cost is over developing these weapons programs," she told reporters in a telephone briefing to preview Tillerson's trip.

Thornton said China had taken "significant steps, ... frankly unprecedented steps" to increase pressure on its neighbor North Korea, but it could do "a lot more" to step up enforcement of existing sanctions and to impose more.

"We would like to see more action faster and more obvious and quick results, but I think we're not giving up yet."

Thornton's remarks contrasted with those of U.S. President Donald Trump, who on Saturday accused Beijing of doing "nothing" to help on North Korea and pointed to the huge U.S. trade deficit with China.

A senior Trump administration official said on Tuesday that Trump was close to a decision on how to respond to what he considers China's unfair trade practices and was considering action that could lead to tariffs or other trade restrictions on Chinese goods.

Thornton declined to comment on any possible action but stressed that despite Trump's tweets, North Korea and the trade issue were not linked in a "transactional," but "in a sort of philosophical way."

"Can we work together jointly on the key security challenge facing Northeast Asia, which is the North Korea challenge?" she said. "If we can work together to do that, surely we can have a productive, mutually beneficial economic relationship in which we both enjoy reciprocal and fair access to each other's markets."

Thornton said Tillerson would continue to press China on the South China Sea issue while in Asia, where the United State has been pressing for rapid adoption of a code of conduct over competing territorial claims.

She said the United States would "certainly" raise human rights with Philippine President Duterte's government.

U.S. criticism of Duterte's bloody war on drugs under Trump's predecessor Barack Obama damaged relations between the long-standing allies. Duterte has remained defiant, accusing critics of "trivializing" his drug campaign with human rights concerns.

Tillerson will also visit Thailand next Tuesday and then Malaysia. His visit to Bangkok will be the first by a U.S. secretary of state since before the military seized power in a 2014 coup.

(Reporting by David Brunnstrom and Yeganeh Torbati; Editing by James Dalgleish)